This invention relates to the field of instrumentation used in controlling and monitoring the movement of a fluid-supported vehicle such as an aircraft, a spacecraft or a submarine, and further concerns the sensing of acceleration of G-forces acting on such a vehicle and the conveyance of magnitude information concerning the sensed forces to a human operator.
For controlling the trajectory of a fluid-supported moving vehicle such as an aircraft, it is frequently desirable to sense and convey to an operator, measurements of the G-forces acting on the vehicle and tending to change its direction of movement. In the case of a moving aircraft, for example, it is especially desirable to know with some degree of precision the magnitude of the acceleration forces tending to increase or decrease the altitude of the aircraft. A record of the incurred acceleration forces for an airframe is also important to prevent continued overstressing of the airframe during combat or aerobatic maneuvers. Preferably such sensing and recording is achieved using the most basic and reliable measurement sensors possible in order to reliably supplement the human operator's sensors--sensors which are easily and intermittently deceived by vertigo and other motion-related considerations. In the case of nuclear submarines, the sensing and display of G forces is also desirable for controlling vessel movement.
In aircraft flight instruments, G-force accelerations along the Z axis, that is, along the spinal column of the pilot or in the directions tending to move the aircraft up or down in a flight path, are of primary interest although sensitivity to forces acting along other axes can be important and can readily be provided by the apparatus of the present invention. A combination of quick readability and accuracy are also desirable in a vehicle-mounted instrument in addition to the normal needs of low mass, small size, wide temperature tolerance and vibration immunity.
Mechanical linkage devices based upon the position changes of a spring-loaded mass in response to applied acceleration forces have been used as airborne sensors and indicators of acceleration forces since the early days of human flight. These mechanically-operated devices are, however, found to be prone to mechanical failures and inaccuracies from vibration, friction, jamming, and mechanical wear to a degree that is undesirable in aircraft equipment.
The increased functional capability, reduced physical size and weight of currently produced electronic devices suggest the incorporation of such devices in G-force sensing instrumentation. As is discussed in more detail below, such electronic sensing equipment is also compatible with the frequent need to remotely monitor or use or record signals relating to the movement of a vehicle.
The development of the integrated electronic circuit, the dichroric liquid crystal display and electrical transducers capable of responding to physical strain or physical movement with a change of electrical properties such as resistance or electrical voltage, have therefore combined to allow significant improvement of the G-force instrumentation used in presently designed vehicles. In particular, these developments have enabled the performance of acceleration sensing and display without the use of components which are subject to complex mechanical movements; such instruments can thereby be largely immune to the debilitating effects of wear, friction and vibration, which were problems in the older mechanical instruments.
The patent art includes several examples of devices which relate to one or more portions of a G-force instrument. This art includes the patent of David E. Weiss, U.S. Pat. No. 3,798,454, which concerns an accelerometer employing a movable inertia weight that is suspended on cantilever springs. The weight and springs are linearly arranged opposite a light source to communicate light between its source and one of several light sensing elements disposed to indicate varying degrees of sensed acceleration. The Weiss apparatus contemplates use of the acceleration sensor for measurement, recording and classification of accelerations for subsequent evaluation, as might be done for vehicle maintenance or safety considerations. The Weiss apparatus also employs a series of counters which record the number of acceleration events exceeding predetermined threshold levels.
Another patent which concerns the acceleration sensing art is issued to Benzion Sandler, U.S. Pat. No. 4,114,453, and concerns several arrangements usable in fabricating an acceleration sensing transducer of the variable electrical resistance type.
Another electrical transducer device is shown in the U.S. Patent of William V. Wright, Jr., U.S. Pat. No. 3,049,685; the Wright transducer is of the general purpose strain measuring type such as might be employed for motion sensing, accelerometers, and other instruments. The Wright strain gauge transducer is of the PN junction type and is configured into the four-leg bridge circuit frequently employed in electrical measurement work.
Another acceleration-responsive apparatus is shown in the patent of H. D. Morris et al, U.S. Pat. No. 3,284,708, wherein is described a dual-range integrating accelerometer that incorporates a digital memory circuit. The Morris apparatus is contemplated for use in moving vehicles such as rocket-propelled spacecraft. The Morris apparatus contemplates integration of an accelerometer signal derived from the electrical output of a position nulling servo-system. The Morris apparatus also contemplates the processing and communication of acceleration data by telemetry without use of a vehicle mounted display.
Another patent which shows the combination of visual display elements, human operator, and G-force acceleration is in the name of Daniel W. Repperger et al, Ser. No. 06/645,390, filed 8/29/84. In the Repperger et al patent there is shown a display arrangement wherein light emitting diodes or other visual stimulus elements are located around the periphery of a human test subject while the subject is exposed to G-force acceleration in the gondola of a test centrifuge. Random light patterns displayed by a first group of visual stimulus elements in this Repperger peripheral display are to be matched or duplicated in a second adjacent group of stimulus elements which are under the control of the test subject. The Repperger apparatus is thereby sensitive to the loss of peripheral field vision on the part of a test subject; this loss is, of course, a result of decreased blood pressure caused by the centrifuge G-force acceleration. The Repperger patent also describes a U.S. Navy originated display used for similar centrifugal testing with somewhat less complexity and accuracy than is achieved in the Repperger apparatus; this Navy apparatus is shown in U.S. Pat. No. 4,421,393, issued to Malcolm Cohen. Neither the Repperger or Cohen patents involve the displaying of G-force magnitudes, however.
The patent art also includes a variety of electrical signal generating transducer elements responsive to acceleration forces according to a plurality of response mechanisms. Typical among these acceleration sensing transducers are the devices described in the patents of Harold D. Morris, U.S. Pat. No. 3,074,279; Eugene C. Huebschmann, U.S. Pat. No. 3,074,280; Tetsuji Shimizu et al, U.S. Pat. No. 3,867,844; Albert P. Youmans, U.S. Pat. No. 4,050,049; Mark L. Stephens et al, U.S. Pat. No. 4,166,269; Andries J. Stoltz, U.S. Pat. No. 4,242,910; and Russell F. Colton, U.S. Pat. No. 4,430,895. Several of these differing accelerometer transducers could be used in the apparatus of the present invention and the disclosure of these transducer patents is therefore hereby incorporated by reference into the present document.